Species spatial distributions in a warm-temperate deciduous broad-leaved forest in China

Spatial distribution is fundamental for understanding species coexistence mechanisms in forest communities.Here we comprehensively explored fine-scale spatial patterns of tree species in a secondary warm-temperate deciduous broad-leaved forest community in north China.Aggregated distribution patterns were predominant.Species functional traits had no significant effects on their spatial patterns.The aggregation intensity decreased with increasing DBH and abundance.The multivariate linear stepwise regression showed that abundance and maximum DBH were correlated with the aggregation intensity.Our results partially confirm that species attributes(abundance,DBH) and habitat heterogeneity may primarily contribute to spatial patterns and species coexistence in this secondary forest.     

Responses of deciduous broadleaf trees to defoliation in a CO2 enriched atmosphere

Relatively little is known about the implications of atmospheric CO2 enrichment for tree responses to biotic disturbances such as folivory. We examined the combined effects of elevated CO2 concentration ([CO2]) and defoliation on growth and physiology of sugar maple (Acer saccharum Marsh.) and trembling aspen (Populus tremuloides Michx.). Seedlings were planted in the ground in eight open-top chambers. Four chambers were ventilated with CO2-enriched air (ambient + 283 micromol mol-1) and four chambers were supplied with ambient air. After 6 weeks of growth, half of the leaf area was removed on a subset of seedlings of each species in each CO2 treatment. We monitored subsequent biomass gain and allocation, along with leaf gas exchange and chemistry. Defoliation did not significantly affect final seedling biomass in either species or CO2 treatment. Growth recovery following defoliation was associated with increased allocation to leaf mass in maple and a slight enhancement of mean photosynthesis in aspen. Elevated [CO2] did not significantly affect aspen growth, and the observed stimulation of maple growth was significant only in mid-season. Correspondingly, simulated responses of whole-tree photosynthesis to elevated [CO2] were constrained by a decrease in photosynthetic capacity in maple, and were partially offset by reductions in specific leaf area and biomass allocation to foliage in aspen. There was a significant interaction between [CO2] and defoliation on only a few of the measured traits. Thus, the data do not support the hypothesis that atmospheric CO2 enrichment will substantially alter tree responses to folivory. However, our findings do provide further indication that regeneration-stage growth rates of certain temperate tree species may respond only moderately to a near doubling of atmospheric [CO2].     

Interannual variability of net ecosystem production for a broadleaf deciduous forest in Sapporo, northern Japan

To estimate net ecosystem production (NEP), ecosystem respiration (R _E), and gross primary production (GPP), and to elucidate the interannual variability of NEP in a cool temperate broadleaf deciduous forest in Sapporo, northern Japan, we measured net ecosystem exchange (NEE) using an eddy covariance technique with a closed-path infrared gas analyzer from 2000 to 2003. NEP, R _E, and GPP were derived from NEE, and data gaps were filled using empirical regression models with meteorological variables such as photosynthetic active radiation and soil temperature. In general, NEP was positive (CO₂ uptake) from May to September, either positive or negative in October, and negative (CO₂ release) from November to the following April. NEP rapidly increased during leaf expansion in May and reached its maximum in June or July. The four-year averages (±?standard deviation) of annual NEP, GPP, and R _E were 443?±?45, 1,374?±?39, and 931?±?11?g?C?m^?2?year^?1, respectively. The lower annual NEP and GPP in 2000 may have been caused by lower solar radiation in the foliated season. During the foliated season, monthly GPP varied from year to year more than monthly R _E. Variations in the amount of incoming solar radiation may have caused the interannual variations in the monthly GPP. Additionally, in May, the timing of leaf expansion had a large impact on GPP. Variations in GPP affected the interannual variation in NEP at our site. Thus, interannual variation in NEP was affected by the incoming solar radiation and the timing of leaf expansion.     

Effects of disturbance history and environmental factors on the diversity and productivity of understory vegetation in a cool-temperate forest in Japan

We assessed the species richness and aboveground productivity of understory plants in nine types of forest stand (116 plots in total) that had different disturbance histories that were combinations of the frequency of plantation (clear-cutting, site preparation, planting), typhoon damage, and selective cutting. We established two 1 m × 1 m quadrats to measure species richness and productivity and one 1 m × 30 m belt to measure species richness in each plot. Canopy leaf area index (LAI), soil NH₄⁺, soil C/N ratio, slope angle, and slope aspect were measured as current environmental factors affecting each plot. The variance in species richness was better explained by disturbance history (69% in quadrats; 86% in the belt) than by current environmental factors. Species richness and the Simpson index decreased as the frequency of plantation increased. In contrast, the variance in productivity was better explained by current environmental factors (82%), especially canopy LAI (45%), than by disturbance history. The relations of species presence and productivity to the explanatory variables differed among species, although there were some common responses within life forms. The effects of disturbance on species diversity remained for 20–80 years. Forest management should therefore take into account the long-term effects of disturbance history to maintain understory plant diversity.     

Photosynthetic responses to lightflecks ofFagus crenata seedlings grown in a gap and understory of a deciduous forest

Photosynthetic responses to a series of 1-min lightflecks (1,000μmol m⁻² s⁻¹) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50μmol m⁻² s⁻¹) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively. The maximum net photosynthetic rate (P _Nmax) and maximum stomatal conductance (g _smax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25μmol m⁻²s⁻¹, the net photosynthetic rate (P ₂₅) and stomatal conductance (g _s25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic rate (P _N ) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase inP _N at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses to lightflecks. The higher ratios ofP ₂₅/P _Nmax andg _s25/g _smax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and stomatal limitations than the gap seedlings under low light conditions. The ratios ofP _N /P _Nmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUE _s) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings when the background PPFD was 25μmol m⁻² s⁻¹. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions than the gap seedlings although the net carbon gain of single lightflecks (CG _s) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUE _s between understory seedlings at a background PPFD of 25μmol m⁻² s⁻¹ and gap seedlings at a background PPFD of 50μmol m⁻² s⁻¹. However,CG _s in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments. This study was funded by the research project, Evaluation of Total CO₂ Budget in Forest Ecosystems, coordinated by the Ministry of Agriculture, Forestry and Fisheries of Japan.     

Responses of deciduous forest trees to severe drought in Central Europe

In 2003, Central Europe experienced the warmest summer on record combined with unusually low precipitation. We studied plant water relations and phenology in a 100-year- old mixed deciduous forest on a slope (no ground water table) near Basel using the Swiss Canopy Crane (SCC). The drought lasted from early June to mid September. We studied five deciduous tree species; half of the individuals were exposed to elevated CO(2) concentration ([CO(2)]) (530 ppm) using a free-air, atmospheric CO(2)-enrichment system. In late July, after the first eight weeks of drought, mean predawn leaf water potential about 30 m above ground was -0.9 MPa across all trees, dropping to a mean of -1.5 MPa in mid-August when the top 1 m of the soil profile had no plant accessible moisture. Mean stomatal conductance and rates of maximum net photosynthesis decreased considerably in mid-August across all species. However, daily peak values of sap flow remained surprisingly constant over the whole period in Quercus petraea (Matt.) Liebl., and decreased to only about half of the early summer maxima in Fagus sylvatica L. and Carpinus betulus L. (stomatal down- regulation of flux). Although we detected no differences in most parameters between CO(2)-treated and control trees, predawn leaf water potential tended to be less negative in trees exposed to elevated [CO(2)]. Leaf longevity was greater in 2003 compared with the previous years, but the seasonal increase in stem basal area reached only about 75% of that in previous years. Our data suggest that the investigated tree species, particularly Q. petraea, did not experience severe water stress. However, an increased frequency of such exceptionally dry summers may have a more serious impact than a single event and would give Q. petraea a competitive advantage in the long run.     

Diversity of secondary woody species in relation to species richness and cover of dominant trees in thermophilous deciduous forests

One of the prominent compositional features of thermophilous deciduous forests of southern Europe is their richness in secondary woody species (AWS). To date, no studies have focused on the diversity and contribution to the ecosystem functions and socio-economic benefits provided by these species. Here, we first characterized species richness and diversity for three main functional groups of AWS, sporadic trees, shrubs and vines, in 53 representative stands of central Italy. Secondly, we explored variations in AWS diversity and composition along a four-level gradient of species richness of dominant trees under comparable site conditions. The 40 AWS taxa recorded showed a remarkable taxonomic singularity at both the genus and the family rank. Dominant tree species richness had no significant effect on AWS species richness and composition, while Shannon diversity of AWS, especially shrubs, was associated with cover of the dominant trees. Each AWS possessed, on average, ca. five ability traits over a total of 13 considered that contributed to important ecosystem functions or expected socio-economic benefits such as wood and food production, conservation of genetic resources (wild crop relatives) and ornamentals. This highlights the key role of AWS, and in particular of sporadic trees, for enhancing multifunctionality of thermophilous deciduous forests.     

Prescribed burning and understory composition in a temperate deciduous forest,Ohio, USA

Since the advent of widespread suppression in the mid-20th century, fire has been relatively rare in deciduous forests of the eastern United States. However, widespread prescribed burning has recently been proposed as a management tool to favor oak (Quercus spp.) regeneration. To examine the potential effects of fire introduction on the understory community, we experimentally burned small plots and simulated aspects of fire at a forested site in southeastern Ohio. Treatments included two burn intensities, litter removal, increased soil pH, and a control. Treatments were arranged in a randomized block design in two landscape positions (dry upland and moist lowland) and two canopy conditions (gap, no gap). Post-fire vegetation was identified to species, and stems were counted 1, 3, and 14 months after burning. Community composition was more strongly affected by fire in upland plots than in lowlands, but was not affected by canopy openness. Both cool and hot burns reduced post-fire seedling emergence of Acer rubrum, a common overstory tree. Hot burns facilitated germination of Vitis spp., Rhus glabra, and Phytolacca americana, species common in disturbed habitats, and increased graminoid abundance. Cool burns and litter removal facilitated germination of Erechtites hieracifolia and Liriodendron tulipifera suggesting that litter removal is the mechanism by which fire favors colonization. These results suggest that fire applied frequently in the Central Hardwoods Region would cause compositional shifts to graminoids and disturbance-adapted forbs by increasing germination from the seed bank. Fire did not favor species with dormant underground buds, as studies in other ecosystems would suggest. Vegetational responses were noticeably weaker in the second year after burning, indicating that a single fire has only a short-term effect.     

Simulating spatial distributions of forest trees by using data from fixed area plots

Cost is a critical factor for managing ecosystems. Common forestinventories are usually carried out at regular time intervals(e.g. every 10 years) and are the basis for management planning.This study investigated the potential of utilizing the dataof common forest inventories for simulating the spatial distributionof forest tree locations. Fixed area plot sample data were takenfrom the University Forest of Pertouli, which is an uneven-agedAbies borisii regis Matf. forest. Using as criterion the indexof dispersion, the tree spatial distribution was characterizedas aggregated. The Neyman Type A distribution, a typical distributionof aggregated populations, was a good fit to the data, whiletree locations simulation was based on the Poisson cluster process.The simulations resulting from the application of fixed areaplot sampling do not incorporate information about the realdistances between the trees, but they can describe adequatelythe spatial patterns of their locations in two-dimensional spaceand seem to be useful tools for managers of forest ecosystems.For similar populations the detection of their aggregation seemsnot to be affected by a considerable decrease of the number(up to 36) and the size (up to 125 m²) of sample fixed-areaplots. This method is cost effective and its use, potentiallyin combination with other methods, could be further investigatedfor its advantages.     

Enhancement of understory productivity by asynchronous phenology with overstory competitors in a temperate deciduous forest

Some saplings and shrubs growing in the understory of temperate deciduous forests extend their periods of leaf display beyond that of the overstory, resulting in periods when understory radiation, and hence productivity, are not limited by the overstory canopy. To assess the importance of the duration of leaf display on the productivity of understory and overstory trees of deciduous forests in the north eastern United States, we applied the simulation model, BIOME-BGC with climate data for Hubbard Brook Experimental Forest, New Hampshire, USA and mean ecophysiological data for species of deciduous, temperate forests. Extension of the overstory leaf display period increased overstory leaf area index (LAI) by only 3 to 4% and productivity by only 2 to 4%. In contrast, extending the growing season of the understory relative to the overstory by one week in both spring and fall, increased understory LAI by 35% and productivity by 32%. A 2-week extension of the growing period in both spring and fall increased understory LAI by 53% and productivity by 55%.     

Carbon dioxide sequestration capability of an unmanaged old-growth broadleaf deciduous forest in a Strict Nature Reserve

The seasonal trend of plant carbon dioxide (CO₂) sequestration is related to the photosynthetic activity, which in turn changes in response to environmental conditions. Great interest has turned to the CO₂ sequestration (CS) potential of temperate forests which play an important role in global carbon (C) cycle contributing to the lowering of atmospheric CO₂ concentration. In such context, the CS of an unmanaged old broad-leaf deciduous forest developing inside a Strict Nature Reserve, and its variations during the year were analyzed considering the monthly variations of leaf area index (LAI) and net photosynthetic rates (N_P). Overall, the total yearly CS of the forest was 141 Mg CO₂ ha^?1 year^?1 with the highest CS value monitored in June (405 Mg CO₂ month^?1) due to the highest LAI (5.0 ± 0.8 m² m^?2) and a high N_P in all the broadleaf species. The first CS decline was observed in August due to the more stressful climatic conditions that constrained N_P rates. Overall, the total CS of the forest reflects the good ecological health of the ecosystem due to its conservative management.     

Changes in aboveground and belowground properties during secondary natural succession of a cool-temperate forest in Japan

Forest development in temperate regions is considered to be a global carbon sink. Many studies have examined forest development after harvesting or fire from aboveground (e.g., biomass) or belowground (e.g., soil nutrient) perspectives. However, few studies have explored forest development from both perspectives simultaneously in cool-temperate forests in Japan. In this study, we examined changes over 105 years in both aboveground and belowground components during secondary natural succession. The aboveground biomass increased for 50 years and reached a plateau in a 105-year-old stand. The N mineralization rate increased during succession for 50 years, but showed a decline in the 105-year-old stand due to the decrease in the nitrification rate in late succession. The percent nitrification (i.e., relative contribution of nitrification to N mineralization) decreased significantly with increasing forest stand age. The N mineralization rates had significant relationships with N concentrations of the dominant tree foliage and litter fall and with the amount of litter fall N. Meanwhile, other belowground properties (i.e., soil pH, phenol concentration, soil microbial respiration, and litter mass loss) did not show any significant relationship with forest stand age. This may be because the soil at the study sites was heterogeneous and consisted of Cambisols and Andosols, the latter of which originally has high organic matter content, and thus may have buffered the effect of the aboveground development. These results indicate that belowground N dynamics are more closely associated with aboveground development than other belowground properties in these forests.     

Light-related competitive effects of overstory trees on the understory conifer saplings in a subalpine forest

To clarify the mechanism by which overstory trees shade understory saplings, we investigated the relationships among light conditions of the saplings (measured as indirect site factor; ISF and direct site factor; DSF), the calculated competition effects of overstory trees on the saplings (W), and relative height growth rate of the saplings (RHGR). We calculated several W values in order to find a W value which can express the light conditions as appropriately as possible, and the results indicated that W explained only 21.9%–24.7% of the total variance of light conditions in the cases where W gave the best fit. In this study, W was calculated based on the basal areas of overstory trees. However, it is known that canopy structure also affects the light regimes in the forest understory, and this might yield the possible errors even within W representing the shading effects most adequately. Therefore, although W significantly represents the shading effect from overstory trees, a great proportion of the variance remained without being explained by W. RHGR was negatively correlated with W, and the W value which had the most adequate explanation of the shading effect also showed the best negative correlation with RHGR. This provides the evidence that the competitive effect of overstory trees on sapling growth is mediated by the shading effect, indicating that competition for light clearly exists within this forest. Such competition for light may closely relate to the well-known phenomenon of gap regeneration in subalpine forests in central Japan.     

Factors determining the distribution of a keystone understory taxon, dwarf bamboo of the section Crassinodi, on a national scale: application to impact assessment of climate change in Japan

The objective of this study was to identify climatic factors determining the distribution of a keystone understory taxon, section Crassinodi of the genus Sasa, and assess the impacts of climate change on the taxon. Relationships between the distribution of sect. Crassinodi and five climatic variables were explored using classification tree analysis. Potential habitats under current climate and future climate in 2081–2100 were predicted. Potential habitats were further divided into suitable and marginal habitats. The predictive accuracy of the model was assessed using receiver operating characteristic analysis and by comparing model predictions with an independent dataset. The model was reasonably accurate. It showed that the warmth index (WI) and snow cover were the most important climatic variables for Crassinodi distribution. Potential habitats were limited to cooler regions with WI <102.7°C month. Suitable habitats were limited to even cooler regions with WI <84.8°C month. The model also showed that areas with deeper snow than previously reported would provide suitable habitats for Crassinodi under some climatic conditions. In 2081–2100, 37.4% of current potential habitats are predicted to become non-habitats because of increases in WI. Most currently suitable habitats are predicted to vanish from western Japan by 2081–2100. Meanwhile, Hokkaido and high-elevation areas of eastern Honshu will sustain suitable habitats. Sect. Crassinodi, which is adapted to less snowy climates, is predicted to be more affected by climate change than sect. Sasa and Macrochlamys, which are adapted to snowy climates.     

Temporal changes in litterfall, litter decomposition and their chemical composition in Sasa dwarf bamboo in a natural forest ecosystem of northern Japan

We investigated the dynamics of litterfall and litter decomposition of Sasa dwarf bamboo (Sasa senanensis) and trees to clarify the characteristics of organic matter and nitrogen cycling between plant and soil in a natural cool-temperate mixed forest ecosystem dominated by an understory vegetation of Sasa. Mean annual Sasa litterfall over the 3-year study period was 164 g m^?2 year^?1, which accounted for approximately 29% of total litterfall. Litter decomposition of Sasa leaf and Sasa culm was significantly slower than that of tree leaf during first and second years. The slow decomposition rates of both Sasa litter types were caused by a significantly higher silicate than in tree leaf. Nitrogen concentration in litter increased as decomposition progressed, especially in Sasa leaf and tree leaf. As a result of the slow decomposition of both Sasa litter types, 111 and 73% of nitrogen to the initial amounts were retained in Sasa leaf and Sasa culm after 3 years, respectively. The amounts of retained nitrogen in Sasa leaf, Sasa culm, and tree leaf after 3 years were 1.29, 0.47, and 3.92 g N m^?2, respectively, indicating that the differences of litter decomposition rates among the litter types influence on the nitrogen cycling in forest ecosystem through the differences of the nitrogen release from litter.     

Differences in leaf phenology between juvenile and adult trees in a temperate deciduous forest

In a deciduous forest, differences in leaf phenology between juvenile and adult trees could result in juvenile trees avoiding canopy shade for part of the growing season. By expanding leaves earlier or initiating senescence later than canopy trees, juvenile trees would have some period in high light and therefore greater potential carbon gain. We observed leaf phenology of 376 individuals of 13 canopy tree species weekly over 3 years in a deciduous forest in east central Illinois, USA. Our objectives were: (1) to quantify for each species the extent of differences in leaf phenology between juvenile and conspecific adult trees; and (2) to determine the extent of phenological differences between juvenile Aesculus glabra Willd. and Acer saccharum Marsh. trees in understory and gap microhabitats. All species displayed phenological differences between life stages. For 10 species, bud break was significantly earlier, by an average of 8 days, for subcanopy individuals than for canopy individuals. In 11 species, completion of leaf expansion was earlier, by an average of 6 days, for subcanopy individuals than for canopy individuals. In contrast, there were no significant differences between life stages for start of senescence in 10 species and completion of leaf drop in nine species. For eight species, leaf longevity was significantly greater for subcanopy individuals than for canopy individuals by an average of 7 days (range = 4-10 days). Leaf phenology of subcanopy individuals of both Aesculus glabra and Acer saccharum responded to gap conditions. Leaf longevity was 11 days less in the understory than in gaps for Aesculus glabra, but 14 days more in the understory than in gaps for Acer saccharum. Therefore, leaf phenology differed broadly both between life stages and within the juvenile life stage in this community. A vertical gradient in temperature sums is the proposed mechanism explaining the patterns. Temperature sums accumulated more rapidly in the sheltered understory than in an open elevated area, similar to the canopy. Early leaf expansion by juvenile trees may result in a period of disproportionately higher carbon gain, similar to gains made during summer months from use of sun flecks.     

日本北海道北部寒温带森林流域林冠层凋落物及其养分归还量的景观格局(英文)

Within a forested watershed at the Uryu Experimental Forest of Hokkaido University in northern Hokkaido, overstory litterfall and related nutrient fluxes were measured at different landscape zones over two years. The wetland zone covered with Picea glehnii pure stand. The riparian zone was deciduous broad-leaved stand dominated by Alnus hirsuta and Salix spp., while the mixture of deciduous broadleaf and evergreen conifer dominated by Betula platyphylla, Quercus crispula and Abies sachalinensis distributed on the upland zone. Annual litterfall averaged 1444, 5122, and 4123 kg.hm^-2·a^-1 in the wetland, riparian and upland zones, respectively. Litterfall production peaked in September-October, and foliage litter contributed the greatest amount （73.4%-87.6 %） of the annual total litterfall. Concentrations of nutrients analyzed in foliage litter of the dominant species showed a similar seasonal variation over the year except for N in P glehnii and A. hirsuta. The nutrient fluxes for all elements analyzed were greatest on riparian zone and lowest in wetland zone. Nutrient fluxes via litterfall followed the decreasing sequence： N （11-129 kg.hm-2.aq） 〉 Ca （9-69） 〉 K （5-20） 〉 Mg （3-15） 〉 P （0.4-4.7） for all stands. Significant differences were found in litterfall production and nutrient fluxes among the different landscape components. There existed significant differences in soil chemistry between the different landscape zones. The consistently low soil C：N ratios at the riparian zone might be due to the higher-quality litter inputs （largely N-fixing alder）.     

Recovery of canopy trees and root collar sprout growth in response to changes in the condition of the parent tree after a fire in a cool-temperate forest

The relationship between the recovery of canopy trees after fire and root collar sprout dynamics was investigated during 1998–2000 in a secondary cool-temperate broad-leaved forest consisting of Quercus mongolica var. grosseserrata and Betula platyphylla var. japonica trees, in northern Hokkaido, Japan, which burned in April 1998. All of the Betula trees that were severely damaged, two-thirds of those slightly damaged, and half of those intact in 1998, died within three growing seasons after the fire. By contrast, half of the Quercus trees that were slightly damaged and half of those severely damaged recovered their foliage, and no slightly damaged or intact trees died during the three growing seasons after the fire. Many Betula trees developed several fruiting bodies of wood-destroying fungi on their stems, irrespective of damage severity. Fungi also infected some of the surviving Quercus, although the crowns tended to recover. Although many sprouting Betula were observed in 1998, the number of sprouts declined rapidly over the study period. Multiple regression analyses showed that the survival and growth of Betula sprouts were positively influenced by the number of sprouts in 1998, damage severity in 1998, and the degree of recover or decline during the study period, and were negatively influenced by parent tree size. On the other hand, a few sprouts of Quercus remained alive. Quercus remained dominant and the dominance of Betula was rapidly reduced after the fire. However, many Betula sprouts remained alive. Stand structure will change drastically for the time being.     

Physiological, morphological and allocational plasticity in understory deciduous trees: importance of plant size and light availability

In a 4-year study, we investigated changes in leaf physiology, crown morphology and whole-tree biomass allocation in seedlings and saplings of shade-tolerant sugar maple (Acer saccharum Marsh.) and intermediate shade-tolerant yellow birch (Betula alleghaniensis Britt.) growing in natural understory light (0.5 to 35% of full sunlight) or in understory light reduced by 50% with shade nets to simulate the effect of gap closure. Leaf physiological parameters were mainly influenced by the light gradient, whereas crown morphological and whole-tree allocational parameters were mainly influenced by tree size. No single physiological, morphological or allocational trait was identified that could explain the difference in shade tolerance between the species. Yellow birch had higher growth rates, biomass allocation to branches and leaf physiological plasticity and lower crown morphological plasticity in unmodified understory light than sugar maple. Sugar maple did not display significant physiological plasticity, but showed variation with tree size in both crown morphology and whole-tree biomass allocation. When sugar maple was small, a greater proportion of whole-tree biomass was allocated to roots. However, physiological differences between the species decreased with decreasing light and most morphological and allocational differences tended to disappear with increasing tree size, suggesting that many species differences in shade-tolerance are expressed mainly during the seedling stage. Understory trees of both species survived for 4 years under shade nets, possibly because of higher plasticity when small and the use of stored reserves when taller.     

Effects of slope and canopy trees on light conditions and biomass of dwarf bamboo under a coppice canopy

Dwarf bamboo, Pleioblastus chino, grows extensively in abandoned coppice woodlands on the Kanto Plain in central Japan and suppresses other understory plants. In order to clarify the factors determining the growth of P. chino, we considered the effect of light conditions under a coppice canopy and examined its relationship with slope aspect, slope angle, and basal area of the trees. The relative photon flux density under the canopy was highly correlated with canopy coverage (R ² = 0.97). The light conditions under the canopy were almost the same at all sites in the summer leafy season regardless of the stand type, while they were remarkably different among the sites and depended on the basal area of evergreen trees in the winter leafless season. The biomass of P. chino on the forest floor was described by the equation: y = 3.18 x ₁ – 0.05 x ₂ + 3.11 (R ² = 0.77, P < 0.01), where y is the log-transformed value of P. chino biomass (gdrymassm^–2), x ₁ is cos at solar noon at the winter solstice, and x ₂ is the canopy coverage during the winter leafless season. is the angle between the suns rays and the normal to the surface and changes with slope aspect and angle. We concluded that light conditions under the canopy in the leafless season had a great effect on P. chino biomass, and that the basal area of evergreen trees and slope characteristics can provide useful guidelines in the control and management of P. chino.